Which organism is associated with the presence of sulfur granules?

Actinomyces israelii is known to be associated with the presence of sulfur granules, which are seen in the pus from actinomycosis infections. These granules, comprised of aggregates of the bacteria, have a yellow-brown appearance and can be an important diagnostic feature. Actinomyces species tend to colonize mucosal surfaces and can lead to chronic infections that form abscesses, especially in the jaw area. The identification of these granules is crucial for diagnosis, as they help distinguish actinomycosis from other infectious processes.

In contrast, the other organisms listed do not typically produce sulfur granules. Staphylococcus aureus is primarily associated with a range of infections but does not form these characteristic granules. Streptococcus pneumoniae, known for causing pneumonia and other respiratory infections, does not produce sulfur granules either. Escherichia coli, commonly associated with gastrointestinal infections, has no relationship with sulfur granule formation. Thus, Actinomyces israelii is specifically the organism linked to the presence of sulfur granules, making it the correct response to the question.